The present invention relates to a method of making an inspection fixture for determining the accuracy of bent tubular parts.
In many industries, and in the aerospace industry in particular, products and machines often require bent tubular parts. Bent tubular parts usually take the form of conduits or pipes that carry gases or other fluids or serve as mounting harnesses for turbine engines and the like. Typically, the conduit or pipe starts out as a straight tube, and is bent into the required shape.
In most applications, the bent tubular parts are required to conform to precise dimensional specifications. One method of determining whether a bent tubular part conforms to the required dimensional tolerances is to construct an inspection fixture having the same profile and dimensional tolerances as an accurately conformed bent tubular part. The bent tubular part to be checked is placed on the fixture. If the bent tubular part can be congruently mounted over the fixture, then the bent tubular part conforms to the required tolerances. If the bent tubular part does not conform to the profile and dimensions of the fixture, then the bent tubular part is rejected as unsuitable.
Prior art inspection fixtures are typically made of blocks of wood or aluminum. Typically, the fixture maker starts with a set of engineering drawings of the desired bent tubular part. He then determines a suitable orientation for the bent tubular part and then typically cuts or forms a series of blocks from wood or aluminum that have flat bottoms, stand vertically upright, and have top surfaces that have profiles that match the shape of respective straight line segments of the bent tubular part. The fixture maker then cuts the end surfaces of the blocks at angles so that the blocks may be angularly fitted together in end-to-end relationship to provide a mounting surface for determining the conformational and dimensional accuracy of the manufactured bent tubular part superposed thereon.
The fitting of the blocks in end-to-end angular relationship defines the profile of the fixture in the X-Y plane when viewed from above. The top surfaces of the blocks will then be cut so as to form the necessary profiles to accommodate features of the bent tubular part such as fittings, couplings, wear sleeves and nuts. The vertical height of the blocks defines the profile of the fixture in the Z dimension. It matches the Z dimension coordinates of an accurately made tube part. The blocks may also be cut to allow for the attachment of yokes and locating means such as end blocks. The blocks are then typically affixed to a base.
The prior art method of making a fixture for determining the accuracy of bent tubular parts may take weeks to prepare. Also, the fixture maker must typically be a skilled machinist or model maker. Accordingly, there continues to exist a need for a method of quickly making an inspection fixture for determining the accuracy of bent tubular parts.